The present invention relates to the production of quaternary ammonium compounds.
Quaternary ammonium compounds are useful as fabric softeners and/or as conditioning agents for the skin or hair. Quaternary ammonium compounds are also useful in other applications, such as softening and debonding of paper products, in the production of fiberglass, car wash performance products, and phase transfer catalysts.
Thus, the present invention relates more particularly to the production of quaternary ammonium compounds wherein the desired quaternary ammonium product is manufactured as a product which can readily be formulated into compositions having these or any other uses and which provide the desired quaternary ammonium compound free of undesirable auxiliary and side products and side reactions.
Quaternary ammonium compounds of the type described herein are frequently synthesized by reacting a corresponding tertiary amine with a quaternizing compound. A portion of the quaternizing compound bonds preferentially to the nitrogen of the tertiary amine, thereby producing the desired quaternary ammonium compound as a cation whose charge is balanced by the anion remaining from the quaternizing agent. The quaternizing reaction is typically carried out in a solvent in which the tertiary amine and quaternizing agent reactants are soluble. The use of such a solvent is considered desirable in order to achieve maximal contact between the reactants and in order to attain and retain fluidity of the reaction mixture at the relatively elevated temperatures at which the quaternization reaction is customarily carried out.
However, the conventional reaction conditions employed when reacting the tertiary amine and quaternizing agent in a solvent lead to conditions during and following the reaction which conditions, while relatively undesirable, have come to be tolerated because they are believed to be outweighed by the benefits of obtaining the desired quaternized product in the yields that can be obtained. Simply put, however, these drawbacks are also considered to be relatively unavoidable in the interest of obtaining the desired quaternized product without resort to conditions and/or reactants which are so expensive or difficult to manage as to render the quaternizing process excessively expensive and inefficient.
For instance, reaction in solvent can lead to formation of a reaction product containing two and sometimes three distinct liquid phases. This result, while it can be dealt with using conventional processing technology, is still to be considered relatively undesirable, because separating the various phases imposes additional processing steps and requires additional equipment. Furthermore, to the extent that the desired product reports to more than one of such phases, recovering the phases separately, as must be done, leads to a sacrifice in the overall yield of the desired quaternary product unless each phase is to be treated separately following separation in order to recover the quaternary product.
In addition, the reaction product is often characterized by being off-color and/or off-odor. This characteristic is believed to be inherent in the reactivities of the tertiary amine and the quaternizing agent, in that the reaction conditions employed to cause the tertiary amine to react with the quaternizing agent are believed to lead inevitably to a certain amount of formation of, for instance, products formed by reaction of the tertiary amine with itself, or with the quaternized product (such as disproportionation reactions) thereby producing a variety of nitrogen-containing end products in addition to the desired quaternary ammonium product. It can be appreciated that separation of the byproducts, which are after all impurities, from the desired quaternary ammonium product is particularly difficult given the similar chemical natures of the byproduct and the desired end product. This problem of reactivities is compounded whenever the solvent chosen has any tendency to engage in competitive reactions or to promote the occurrence of competitive side reactions. Thus, the conventional technology of quaternizing reactions requires a careful selection of the proper solvents to minimize the contribution of the solvent system to the tendency of the amine to undergo competitive side reactions.
Accordingly, there remains a need in this area of technology for a process for forming desired quaternary ammonium compounds while suffering at most a minimal tendency for the reactants to engage in competitive side reactions. This need is emphasized by the fact that formulators of end products such as fabric softeners, hair conditioners, and skin conditioners, prefer to obtain the quaternary ammonium ingredients essentially in the form, and in particular, in association with the solvent system, in which the quaternary ammonium compounds have been synthesized. This feature permits the formulators to avoid having to recover the quaternary ammonium compound from one solvent system and then to reincorporate it into another solvent system or into the final composition for use by the consumer. This fact, however, severely restricts the choice of solvent systems available to the manufacturer of the quaternary ammonium compound. Thus, there remains a particular need for a process for forming quaternary ammonium compounds useful in applications such as fabric softeners, hair conditioners, and skin conditioners, which produces such quaternary ammonium compounds in a solvent system compatible with the intended end use of the quaternary ammonium compound.